CISA KEV · catalog date Nov 3, 2021 · first observed Jul 19, 2026
Evidence dossier
CVE-2021-26858
Microsoft Exchange Server Remote Code Execution Vulnerability
Exploited in the wild (CISA KEV since Nov 3, 2021). microsoft reports CVSS 3.1 7.8. EPSS estimates 89.5% exploit likelihood as of Aug 18, 2026.
As of Aug 27, 2026
Normalized restatement
Microsoft Exchange Server Remote Code Execution Vulnerability
- State
- PUBLISHED
- Published
- Mar 2, 2021
- Updated
- Oct 21, 2025
- Evidence coverage
- 92%
Evidence chronology
What was known when
- Source dateSource date omittedFirst observed by CASCACISA-ADPOriginal evidence ↗
Record text: CISA ADP Vulnrichment
Inspect raw assertion
- Field
container- Value
- CISA ADP Vulnrichment
- Source dateSource date omittedFirst observed by CASCACVE ProgramOriginal evidence ↗
Record text: CVE Program Container
Inspect raw assertion
- Field
container- Value
- CVE Program Container
- Source dateSource date omittedFirst observed by CASCAmicrosoftOriginal evidence ↗
Record text: Microsoft Exchange Server Remote Code Execution Vulnerability
Inspect raw assertion
- Field
container- Value
- Microsoft Exchange Server Remote Code Execution Vulnerability
- Source dateFirst observed by CASCACISA KEVOriginal evidence ↗
Exploitation cataloged: Microsoft Exchange Server Remote Code Execution Vulnerability
Inspect raw assertion
- Field
observed_exploitation- Value
- Microsoft Exchange Server Remote Code Execution Vulnerability
- Source dateFirst observed by CASCAFIRST EPSSOriginal evidence ↗
EPSS score: 89.51% probability · 99.77th percentile
Inspect raw assertion
- Field
model_probability- Value
- Probability 0.895090000000; percentile 0.997740000000
FIRST EPSS · score date Aug 18, 2026 · 99.8th percentile · first observed Aug 18, 2026
microsoft · CVSS 3.1 · first observed Jul 19, 2026 · same-version scores align in this snapshot
Evidence detail
Source limits and decisions
Why each evidence state has this value
casca-unknown-reasons-v1Eligible evidence is present for this bounded claim.
- Revision
- evidence-policy-v1.1.0
- Cutoff
- Aug 27, 2026
- Resolution
- None
Eligible evidence is present for this bounded claim.
- Revision
- evidence-policy-v1.1.0
- Cutoff
- Aug 27, 2026
- Resolution
- None
Eligible evidence is present for this bounded claim.
- Revision
- casca-direct-cvss-eligibility-v1
- Cutoff
- Aug 27, 2026
- Resolution
- None
The cited source assertion is retained while canonical product linkage remains open.
- Revision
- casca-factor-d-obligations-v1
- Cutoff
- Aug 27, 2026
- Resolution
- Resolve identity
Source comparison
Who said what
CISA ADP Vulnrichment
Inspect raw assertion
- Field
container- Value
- CISA ADP Vulnrichment
CVE Program Container
Inspect raw assertion
- Field
container- Value
- CVE Program Container
Microsoft Exchange Server Remote Code Execution Vulnerability
Inspect raw assertion
- Field
container- Value
- Microsoft Exchange Server Remote Code Execution Vulnerability
Microsoft Exchange Server Remote Code Execution Vulnerability
Inspect raw assertion
- Field
observed_exploitation- Value
- Microsoft Exchange Server Remote Code Execution Vulnerability
89.51% probability · 99.77th percentile
Inspect raw assertion
- Field
model_probability- Value
- Probability 0.895090000000; percentile 0.997740000000
Applicability
Cited product scope
Grouped from 1 configuration nodes in this exact snapshot. Visual grouping is navigational; asset exposure and root cause require cited evidence.
Identity source boundaries
- Cpe dictionary1,775,266 records · observed through 2026-07-21T06:45:29.809Z
27d65b0f-b718-4b4f-bb79-c47c68d09dfa - Cpe match643,502 records · observed through 2026-07-21T08:13:17.697Z
955dae73-7302-438b-aee1-058d7cc5d48e
25 scope groups
Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.00.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.00.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.00.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]product-d87daca995d075bf30565cc429e7242a47683272975068df1d327ec1d8ff609cLinked exactInspect raw assertions
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_13:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 7
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
4df5bdb5-205d-4b64-a49a-0152afcf4a13
cpe:2.3:a:microsoft:exchange_server:2013:sp1:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 3
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
0c21f84b-e99c-451d-9eaf-6352fd2b0eaf
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 13
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
28fca0e8-7d27-4746-9731-91b834ca3e64
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_15:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 9
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
ca2ce223-aa49-49e6-ac32-59270eff55ad
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_1:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 17
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
051de6c4-7456-4c42-bc51-253208aadb4e
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_9:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 15
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
69af19dc-3d65-49a8-a85f-511085cdf27b
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_14:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 8
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
55284cf7-0d04-4216-83fe-4b1f9ca94207
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_11:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 5
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
9be04790-85a2-4078-88ce-1787bc5172e7
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_12:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 6
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
ccf101be-27fd-4e2d-a694-c606bd3d1ed7
cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 2
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
da166f2a-d83b-4d50-ad0b-668d813e0585
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_7:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 23
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
36ce5c6d-9a04-41f5-ae7c-265779833649
cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_22:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 1
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
751fd35f-2ecd-4b75-9589-988cc6ad3058
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_4:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 20
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
73b3b3fe-7e85-4b86-a983-2c410ffef4b8
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_10:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 4
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
63e362cb-cf75-4b7e-a4b1-d6d84afcbb68
cpe:2.3:a:microsoft:exchange_server:2019:-:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 16
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
40d8a6db-9225-4a3f-ad76-192f6cccf002
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_8:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 14
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
075e907f-af2f-4c31-86c7-51972be412a1
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_2:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 18
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
ee320413-d2c9-4b28-89bf-361b44a3f0ff
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_6:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 22
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
d4ab3c25-cea8-4d66-aee4-953c8b17911a
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 24
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
44ecf39a-1de1-4870-a494-06a53494338d
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_16:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 10
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
4830d6a9-af74-480c-8f69-8648cd619980
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_17:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 11
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
079e1e3f-ff25-4b0d-ac98-191d6455a014
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_5:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 21
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
8a9fb275-7f17-48b2-b528-be89309d2af5
cpe:2.3:a:microsoft:exchange_server:2010:sp3:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 0
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
3e5ea9ad-1e84-4ab5-a1ef-3b9f2ac84755
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_18:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 12
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
29805ec7-6403-44b9-91ec-109c087e98eb
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_3:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 19
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
104f96dc-e280-4e0a-8586-b043b55888c2
Affected-product evidence
Accepted scope and product mapping
1 canonical links · 1 source-reported links
vendor-01299a5a765aea70faa05f2d06e0c26a5d498fd34553e868d89e8a43b31864db · product-d87daca995d075bf30565cc429e7242a47683272975068df1d327ec1d8ff609c
- Source class
- Nvd cpe vulnerable target
- Assertions
- 25
- Mapping revision
- cpe23-exact-mapping-v1
- Observed cutoff
- Aug 27, 2026
Retained assertion IDs
034b01ad-200e-4122-aca9-9b95db63602908af8b07-b38b-4699-b077-8ebd308a92ad1b503b03-f5ef-4a16-b6d7-0bf3cb2c85d02848f2cc-e1ff-4f9a-a3f0-86d36f257b5f30c05096-20f3-4a17-a7e3-31624a4a73be3a4c58e7-2d0e-491b-9c93-3e1fc408cc11439020ed-c5d7-439d-a18c-0e638218a7265b1425ea-ca99-4e21-a51a-ff37f9ba44656369fe5d-d428-47f2-8b8d-601fae610ce078e595c9-a7e3-44b9-ad17-010ff562c2d77fc744ee-63bc-4bd7-9d03-04af998c19418fef70d3-9f38-42ef-8b21-9dcf6740d78394333900-7616-467d-a795-0cc2b177b91394ed7c78-5968-4165-8ff5-d655693a51d89a25fccb-c16d-4071-a4b4-cf236b4cfd959f28bfaf-827c-4ecd-878c-b1e4e888f95ea66cd29b-279b-4842-9cb3-1cd3b9f7a4a3b48ad283-ff06-4d38-8740-4ff277b74815b4c59def-ae87-4b31-8268-5667f3d5a7eebfdb1330-f18d-461f-8219-bfc49546e020da4f1c2a-c995-4a3f-8345-ee3e8f3f83abe31c432e-d2e1-429a-bc66-d9b903d4dac5f6dc3f01-e5d1-4596-94a5-b661019b0359f789b09e-72e0-4684-acf7-3afdd0507003fd1924b6-beb9-4827-892f-e97c950e63e1Canonical linkage remains open; the cited source assertion is retained below.
Vendor specified only by source · Product specified only by source
- Source class
- Direct cve affected
- Assertions
- 24
- Mapping revision
- cpe23-exact-mapping-v1
- Observed cutoff
- Aug 27, 2026
Retained assertion IDs
067a3744-85c8-4c6c-b6a4-12028bc9bc6312a68dcc-9909-4003-919a-b45360f09c921a297eee-16bd-469d-a9bf-27002748ec281c5149a9-144c-4748-bafa-97116fd6165723358bfa-b615-4e39-afae-4666e4063de525397cde-5046-4918-8691-fdd09cf4a0ac30274db8-f7e7-42ec-a0ff-b0a9b524e7d072811f6a-2699-4ecf-9014-a9c8fc68ff95729361d7-711d-42c7-ab56-9b584498ce637bd8e774-3646-4410-ae19-aa2056652dfa83b02218-d8b5-49b8-85f7-7b40b687298b8bbfc62d-d8ec-47c2-8d35-bdb4b6843cfc9025d976-ad5d-4001-88b9-530663898cce90e4d5cd-d341-46b7-bfb0-96b24dda2ac39e235b7d-5434-444c-a379-87c9e4bb26aaa02dcd91-f78d-4e24-bd33-6bb3e8690fb1a3e98a82-1149-4d72-b294-c91b37631cb3a9103a25-f368-4816-9617-dfff1d4c39b5af48af8d-97ed-48b6-8212-7cfe87ac2e03c6fdba09-2237-4be6-9a19-c01a260357a5e6d14197-54e5-4191-ad04-ca25190e3ee2e78bc7f9-ba14-4262-86d3-043ce006485af0f5920d-e01f-41fa-9ad3-184dd874e290f208154e-d9d2-481d-8856-5949d37d106cAssessments
CVSS by origin
AV:N/AC:M/Au:N/C:P/I:P/A:PCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:CDirect CVE/CNA normalized decisions
microsoft
CVSS 3.1 · Primary · Original assertion · rank 1
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C- Validation
- Valid match
- Recomputed
- 7.8
- Decision reason
- Evidence supported
- Policy
- casca-direct-cvss-eligibility-v1
Assessments are retained side by side under closed precedence. Cascade never averages CVSS.
Evidence boundaries
- KEV membership is authoritative for the catalog, not proof of exposure in any environment.
- EPSS is a dated model probability and not an individual-environment prediction.
- Affected or fixed status applies only to the exact cited product and version scope; remaining scope stays source-scoped.
- NVD-carried upstream facts remain derivative; independent corroboration requires a separately authored source.
- Only NVD metrics validated under the generation-bound calculator are Public Priority eligible; direct CVE record metrics remain display-only.
- NVD CVSS source eligibility is closed: NVD-authored, exact record-source, or registered same-CVE container origin; unmapped sources remain display-only.
- Core replay supports the active and immediately prior generation; retrospective valid-at replay is deferred.
- OSV aggregation and OSV-converted NVD material are not independent corroboration.
- Red Hat facts are vendor assertions for the exact supplied products.
- Nonmembership and not-yet-observed states are not proof of safety.